Click on possible answers in the right column to hide/show them on the graph. You can also hover over any line to see current value at that time. Graphs will begin to show data one hour after the question has been open. The Historical Trend chart does not display all prices ever reached since it is only updated at discrete time intervals, (hourly/daily/weekly, depending on the date range).
This year, the Kentucky Derby has a new set of qualifying rules. For current standings, as well as links to explanations of how this works, see http://www.drf.com/news/kentucky-derby-2013-point-standings
It remains true that no more than 20 horses will run. More than 20 possibilities are listed here, and there is always a chance that a "Field" horse (one not listed here) will qualify.
The format of the answers is as follows:
Horses with a number and odds, e.g. "1 Verrazano (4-1)" are the 20 horses currently being rated as top contenders by the Daily Racing Form (DRF). http://www.drf.com/events/kentucky-derby-top-20-churchill-downs
The odds given are those listed in the DRF, and are only estimates.
Horses with no odds given, and a number starting "#" are other horses that are currently in the top 20 list of the point standings, so may or may not qualify. There are still 4 important prep races to be run over the next 2 weeks, and the results of those races will have a big influence on the standings.
All of the information given with the horses' names is as of March 29, and I may or may not update it to reflect changes over the next month. When the final Derby field is announced, I will pay out horses that will not run at zero.